1. Field of the Invention
The present invention relates to a wet sensor and a wet annunciator to be used to a diaper (a moisture-generating member) for a baby, a toddler, an old man, or the like.
2. Description of the Related Art
While a diaper (a moisture-generating member) is used normally to a baby or a toddler, the number of old users of diapers is now increasing. A diaper which gets wet due to excretion, if left as it is, may cause uncomfortable odor and skin irritations. Thus, it is ideal that a wet diaper is immediately changed for a new diaper. However, in case a mother takes care of her child, since she changes a diaper for the child according to a sign shown by the child, it is less likely that a wet diaper is left as it is. With regard to a bed-ridden old man in a geriatric hospital and the like, on the other hand, in case a diaper is only changed at a regular interval, especially for the bed-ridden old man, since an excretion interval is different among individuals, the change of the diaper at a regular interval does not meet their requirements. Further, a wet diaper over several excretions being left as it is may occur. It is not preferable for the health and sanitation to leave a wet condition for a long time.
Accordingly, various kinds of devices for electrically detecting a condition that a diaper gets wet and for informing the user or others of the wet condition have been devised. One of them is disclosed in Japanese Utility Model Laid-open No. Sho 60-181311, in which one end portion of a back sheet impermeable to water is extendedly provided so as to cover a water absorbing layer, metal layers are adhesively formed so as to sandwich the portion which is provided extendedly, and, the back sheet and the metal layers, between which the water absorbing layer is sandwiched, form a capacitor, wherein a change of an electrostatic capacity depending on a quantity of adsorbed water in the water absorbing layer is picked up to make known when the diaper gets wet.
Another example is disclosed in Japanese Utility Model Publication No. Hei 6-21018, in which the structure of a sensor for detecting a wet condition mentioned in the above is disclosed specifically. In this example, metal layers are provided in parallel with each other leaving a predetermined space therebetween along the longitudinal direction of a rectangular back sheet impermeable to water. Only one of the metal layers is coated so as to become an electrically insulated layer, and upper surfaces of the two metal layers are coated with a front sheet permeable to water. With this structure, a change of the capacitor formed by the metal layers, the electrically insulated layer, and the front sheet is detected to make known when the diaper gets wet.
Still another example is disclosed in Japanese Utility Model Publication No. Hei 6-7698, in which a moisture sensor with a conductive front surface adsorbing layer is attached to a body of a disposable diaper made of paper, and an output signal of the sensor is sent out to the outside as a radio wave.
These techniques have made it possible to inform a person who looks after the user of the diaper or the like that the diaper gets wet. However, in all of these techniques, since a metal layer is disposed in the diaper, to discard the diaper means to discard the sensor. Accordingly, the sensor may not be used over a long period. It is therefore an object of the present invention to provide a wet annunciator and a wet sensor for use of the wet annunciator which are improved with regard to the point mentioned above.